The present invention relates to a control apparatus, a control method, and a control program for an elastic actuator drive mechanism, which serve for controlling operations of a drive mechanism that drives by an elastic actuator such as a fluid pressure drive actuator driven by deformation of an elastic body.
In recent years, since cell production factories have become widespread, and so on, development of robots that cooperate with person has been performed energetically. Unlike conventional robots that operate in work areas for robots and separated from areas where a person is present, it is necessary for such a robot that cooperates with the person to co-exist with the person. Accordingly, the robot that cooperates with the person is different in required specifications from a conventional industrial robot and the like.
First, in the conventional industrial robot, an electric motor or a decelerator is used, and by high-gain feedback control, hand position accuracy as high as 0.1 mm of repetition accuracy is realized. However, in many cases, a mechanism driven by such an electric motor has high rigidity and is poor in flexibility, and is problematic in terms of safety.
As opposed to this, in the robot that cooperates with person, such safety is regarded as important that the robot cannot harm humans at the time of contacting the humans. Hence, it cannot be said that the mechanism driven by the electric motor, as in the conventional industrial robot, is suitable for the field of domestic robots where the safety is regarded important, and a flexible and safe robot arm is required.
Regarding these issues, for example, there is proposed a robot arm that uses a McKibben-type pneumatic actuator. The McKibben-type pneumatic actuator has a structure, in which a constraining means formed of fiber cords is arranged on an outer surface of a tubular elastic body made of a rubber material, and both end portions of the tubular elastic body are hermetically sealed by sealing members. When an internal pressure is given through a fluid injection/ejection means to an inner space of the tubular elastic body by a compressive fluid such as air, the tubular elastic body attempts to expand mainly in a radius direction. However, by a function of the constraining means, a motion to expand in the radius direction is converted into a motion in a central axial direction of the tubular elastic body, and then, an overall length of the tubular elastic body contracts. This McKibben-type actuator is mainly formed of the elastic body, and accordingly, is provided with flexibility, and has such features in being a safe and lightweight actuator.
Secondly, since the conventional industrial robot operates in a space separated from a person, it is considered the safest for the conventional industrial robot to instantaneously stop its operation, for example, when a sensor failure and the like occur.
As opposed to this, in the case of the robot that moves in the same space with the person, it is not always the safest for the robot to instantaneously stop the operation when the sensor failure and the like occur. For example, when the robot operates cooperatively with the person, in the case where the robot suddenly stops, the person who operates cooperatively with the robot cannot stop quickly, and is considered to fall in a dangerous state. However, when the sensor has failed, information necessary for the operation control cannot be gained, and there has been an issue that it is difficult to continue the operation.
For such a sensor failure as described above, a conventional technique discloses a control apparatus that controls the robot by reading previously instructed and stored data in place of a sensor signal (Japanese Examined Utility Model Publication No. H08-1819). Moreover, in a robot including a distance sensor and a plurality of movement mechanism position detectors, a conventional technique discloses a movement control apparatus including a computing unit that obtains the same alternative signal as a correct movement mechanism position signal, which is to be originally outputted by a broken movement mechanism position detector, based on a sensor signal from the distance sensor and movement mechanism position signals from normal movement mechanism position detectors (Japanese Examined Patent Publication No. H05-55279).
However, although the instructed data that serves as an alternative to the sensor signal becomes necessary in advance in the technique of Japanese Examined Utility Model Publication No. H08-1819, there has been an issue that it is difficult to assume every operation of the robot in advance, and it is difficult to prepare the instructed data. Moreover, in the technique of Japanese Examined Patent Publication No. H05-55279, there has been an issue that a correct alternative signal cannot be computed in a robot that does not have the distance sensor.